Also note that a lot of the issues have to do with the fact that much/most higher-end DDR2 RAM is sold according to speed/latency measured under non-standard conditions (e.g. higher DIMM voltage than the 1.8V DDR2 standard). This post may help clarify things: http://forumz.tomshardware.com/hardware/modules.php?name=Forums&file=viewtopic&p=1249881#1249881
Unfortunately, some memory manufacturers have focused so much on these non-standard conditions that their modules sometimes won't work at all under standard conditions! Hence, the reports of problems/incompatibility.